This invention relates broadly to a method for removing engine deposits from turbine components, in particular turbine disks and shafts, using a cleaning composition. This invention further broadly relates to a cleaning composition for use in this method that comprises an aqueous solution comprising a nitrate ion source and a bifluoride ion source.
In an aircraft gas turbine engine, air is drawn into the front of the engine, compressed by a shaft-mounted compressor, and mixed with fuel. The mixture is burned, and the hot exhaust gases are passed through a turbine mounted on the same shaft. The flow of combustion gas turns the turbine by impingement against the airfoil section of the turbine blades, which turns the shaft and provides power to the compressor. The hot exhaust gases flow from the back of the engine, driving it and the aircraft forward. The hotter the combustion and exhaust gases, the more efficient is the operation of the jet engine. Thus, there is incentive to raise the combustion gas temperature.
The turbine engine includes turbine disks (sometimes termed “turbine rotors”) and/or turbine shafts, a number of blades mounted to the turbine disks/shafts and extending radially outwardly therefrom into the gas flow path, and rotating, as well as static, seal elements that channel the airflow used for cooling certain components such as turbine blades and vanes. As the maximum operating temperature of the turbine engine increases, the turbine disks/shafts and seal elements are subjected to higher temperatures. As a result, oxidation and corrosion of the disks/shafts and seal elements have become of greater concern.
Turbine disks/shafts and seal elements for use at the highest operating temperatures are typically made of nickel and/or cobalt-base superalloys selected for good elevated temperature toughness and fatigue resistance. They have resistance to oxidation and corrosion damage, but that resistance is not sufficient to protect them at the operating temperatures now being reached. Over time, engine deposits, primarily in the form of nickel oxides and/or aluminum oxides, can form a coating or layer on the surface of these turbine components. These engine deposits typically need to be cleaned off or otherwise removed.
Accordingly, it would be desirable to be able be able to effectively and efficiently clean and remove engine deposits, especially engine deposits comprising metal oxides, from turbine components that comprise nickel and/or cobalt-containing base metals. It would be especially desirable to be able to clean and remove such engine deposits in a manner that does not excessively or substantially remove or alter the nickel and/or cobalt-containing base metal of the turbine component. It would further be desirable to be able to formulate a composition that is effective and efficient in cleaning and removing such engine deposits.